Workpiece support



Filed Jan. 16, 1963 CARL H. WESTBERG INVENTOR.

United States Patent 3,197,925 WORKHECE SUPPORT Cari H. Weather-g, Webster, Mass, assignor to The Heaid Machine Company, Worcester, Mass., a corporation of Deiaware Filed Jan. 16, 1363, Ser. No. 251,944

4 Claims. Cl. 51-236) This invention relates to a grinding apparatus and, more particularly, to apparatus arranged to support a workpiece for the generation of a surface of revolution by the abrasive process.

In the grinding of workpieces, particularly the internal grinding of small workpieces such as miniature ball hearing races, a number of problems are presented in holding the workpiece during grinding and in loading an unfinished workpiece into the work area. It is common practice to support the outer surface of the workpiece with three-point contact and to use a fixed shoe at the portion of the workpiece opposite the point where the abrasive wheel pressure takes place. Two other supports, which may be in the form of disks (one above and one below the workpiece), provide the remainder of the support. Conventionally, the upper disk is movable and is spring-biased toward the workpiece. An unfinished workpiece engages and cams this upper disk to move it out of the way, so that the finished workpiece leaves and the unfinished workpiece moves into the work area. This sort of work support can cause instability of the workpiece in that the variation of wheel pressure longitudinally of the bore being ground, because of the reciprocation of the abrasive wheel, causes theworkpiece to move angularly with respect to the axis of the wheel. The result is that the bore is ground with a slight taper, which is an undesirable situation. If the contact point of the upper wheel is moved around the workpiece to a position where the stability of the workpiece is increased, it is ditlicult, if not impossible, to load and unload workpieces. When machines of this type have been built, it has been found that the finished workpiece does not leave thework area but remains jammed between the two disks and thus prevents the upper disk from engaging the unfinished workpiece to hold it in place. These and other diificulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a workpiece support in which small workpieces are held in place with a high degree of stability, so that reciprocation of the abrasive wheel does not cause movement of the workpiece and does not cause resultant taper in the finished surface.

Another object of this invention is the provision of a workpiece support, particularly for the internal grinding of bores, in which the workpiece is held with a high degree of stability and yet loading and unloading may take place without difficulty.

A further object of the present invention is the provision of a workpiece support for holding miniature workpieces in which loading may take place positively without finished workpieces remaining in the workpiece support and preventing normal operation.

It is another object of the instant invention to provide a workpiece support in which a small workpiece having both an external surface of revolution and internal surface of revolution may be finished by the abrasive process,

3,133,925 Patented Aug. 3, 1965 loading and unloading, which workpiece support is simple and inexpensive to manufacture and is capable of a long life of useful service' With these and other objects in view, as will be apparent to those skilled in the art, the i vention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms as illustrated by the accompanying drawings in which:

The single figure shows an elevational view of a grinding apparatus embodying the principles of the present invention as observed in the direction of the axis of the workpiece and the abrasive wheel.

Referring to the drawing, it can be seen that the grinding apparatus, indicated generally by the reference numeral 19, is mounted on the workhead table 11 of a grinding machine. This grinding machine is of the type shown and described in the patent application of Townsend et al. Serial Number 158,974, filed December 13, 1961, now Patent No. 3,131,517, dated May 5, 1964. A workpiece 12 is shown supported in the workpiece support and is indicated as having an outer surface 13 which is a surface of revolution and an inner surface 14 which is also a surface of revolution; this workpiece may, for instance, be the outer race of a miniature ball bearing. In any case, it is the internal surface of revolution 14 which is to be finished, according to the preferred embodiment of the invention.

The workpiece support is shown as having a base 15 with an upstanding abutment 16 on which is mounted an arm 17. The arm is attached to the abutment by a horizontal pivot pin 18 which extends parallel to the axis of the workpiece 12. Rotatably carried at one end of the arm 17 is a disk 19 which engages the outer surface 13 of the workpiece 12. Another disk 21 is keyed to a shaft 22 extending through the base and having mounted at its outer end a pulley 23 driven through a belt 24 by a workhead motor (not shown). The disk 21 contacts the outer surface 13 of the workpiece 12 at a point below its axis. Bolted to the surface of the base 15 is a member 25 having a hardened metal shoe 26 which engages the outer surface 13 of the workpiece 12 at a point beside its axis.

The member 25 has a straight, horizontal upper edge along which reciproc-ates a loading finger 27. The arm 17 is made up of a first part 28 and a second part 29 which are pivotally connected by a hinge pin 31. The first part 28 consists, in turn, .of a portion 32 which is the actual part containing the hinge pin 18, One end I of the portion 32 on the side of the pin 18 away from wherein the work support consists of a fixed shoe and two disks, wherein the workpiece is not moved during the grinding operation, and wherein loading and unloading may take place in a positive manner.

It is a further object of the invention to provide a work-' piece support for operating miniature workpieces with a high degree of stability and a minimum of difliculty in the second part 7.9 is engaged by a light coil spring 33 which is continually under compression and which biases the arm in a counter-clockwise direction of rotation about the hinge pin 18. Also engaging the outer end of the portion 32 is a heavy coil spring 34 pressing against a plate 35 which is connected to a piston 36 by a piston rod 37. The piston slides in a cylinder 38 which is attached to the underside of the portion 32 of the arm, so that the cylinder and .piston and the spring 34 extend between the outer end of the portion 32 and a top surface of the base 15. Extending from opposite ends of the cylinder 38 are hydraulic conduits 3? and 41. The first part 28 is also provided with a portion 42 which is fork-shaped with a shank bolted to the part of the portion 32 which is on the workpiece side of the pivot 18. The second part 29 of the arm is pivoted between the two tines of the fork by the pin 31 extending between them. Bolted across the bifurcation is a bar 43 through the center of which extends a stop screw 44 'which is locked in place by a lock nut 45. Extending between the bifurcations of the portion 42 is an inclined, hardened-metal insert =19 4-6 which is engaged by an adjustable screw 47 extending through the outer end of the first portion 29 of the arm and locked in place by a lock nut 48. A coil spring 49 extends around the screw 47 between the insert 46 and the facing surface of the outer end of the second portion 29 of the arm. The inner end of the second portion 2% is provided with a shaft 51 on which the disk 19 is rotatably mounted. The outer end of the second portion 29 is provided with a stop finger 52 adapted, on occasion, to engage an adjusting stop screw 53 which extends upwardly through a horizontal shelf 54 which is formed on the surface of the base 15 and which is provided with a lock nut 55. The disk 19 is provided with a pulley 56 driven through a belt 57 connected to the same motor as the belt 24. r The workpiece sup-port is similar. in its operational function to the workhead described in the above-mentioned patent application Serial Number 158,974. This means that the spring 34 is under compression and the disk 19 is forced downwardly with a force which is limited by the compression of the spiing 34. During loading, however, the hydraulic pressure is reversed and the pressure appears on the conduit 41 and throws the piston 36 to the upper end of the cylinder, thus relieving the compression on the spring 34. The spring 33, however, is selected to retain a spring action even in this condition and causes a slight downward-or counter-clockwise spring motion in the elements.

The operation of the invention will now be readily understood in view of the above description. With the workpiece 12 in place, the disk '21 contacts the undersurface of the workpiece and is driven by the belt 24 through the pulley 23 of the shaft 22. This causes a counterclockwise rotation and, therefore, a clockwise rotation of'the workpiece 12. The workpiece is pressed against the shoe as which, because of the friction between the two, restricts somewhat the movement of the workpiece. The disk '19 contacts the outer surface 13 of the workpiece 12 at a position approximately 135 away from the contact-with the shoe 26. This forces the workpiece toward the shoe 26 and toward the drive disk 21. The disk 19 is driven and, therefore, assists in the rotation of the workpiece 12. In accordance with usual nomenclature, the shoe 26 contracts the outer surface of the workpiece at the 3:00 oclock position, the disk 21 contacts at the 6:00 oclock position, and the disk 19 contacts at somewhere around the 10:30 oclock position. Even when the abrasive wheel is reciprocating against the inner surface 14 of the workpiece, it is impossible for the wheel to incline the workpiece relative to the normal axis, so that tapering is not encountered:

When the workpiece is finished and it is desired to load a new unfinished workpiece in the work area, the machine reverses the oil to the cylinder 38 so that the piston 35 occupies an upper position. This rotates the arm slightly in a clockwise direction. Because of the spring 49, however, the disk 19 is maintained in contact with the workpiece, but then occupies a position at the 12 oclock position on the workpiece. Then, when I the loading finger 27 approaches the work area pushing anew workpiece ahead of it, the new workpiece engages the surface of the disk H and pushes it upwardly away from the old workpiece against the spring pressure 49 and against the spring pressure 33. It should be noted that, since the spring 33 is the weaker, it will dominate the situation and give a relatively soft action on the disk 19, so that it is readily pushed away. Because of the disk 19 being located at the 12:00 oclock position (shown in dotted lines), the old workpiece readily falls outwardly over the surface of the lower disk 21.

The stop 53 may be engaged, on occasion, by the finger 52; this assures that the disk 19 does not strike the disk 21 when no workpiece is interposed between them. The stop screw 44 may engage the upper part of the second part 2.9 of the arm to limit collapse of the toggle. Furthermore, the engagement of the stop screw 47 with the insert 46 limits the movement of the toggle in the other direction.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent, 182 a 1. Apparatus for supporting a workpiece having a surface of revolution, comprising (a) a base,

(b) a first member mounted on the base adapted to contact a position on the surface of the workpiece,

(c) a second member mounted on the base adapted to contact the surface of the workpiece at a position substantially spaced from the position of contact of the first member,

(d) a third member mounted on the base adapted to contact the surface of the workpiece at a first position substantially opposite the midpoint between the position of contact of the first member and the position of contact of the second member, and

(e) an articulated arm having two hinged portions spring-biased relative to each other and also to the base supporting the third member in such a manner that, on occasion, it contacts the surface of the workpiece at a second position which is substantially opposite the position of contact of the second member and is movable radially away from the said second position.

2. Apparatus as recited in claim 1, wherein the said articulated arm is pivoted to said base and carries the third member at one end.

3. Apparatus as recited in claim 1, wherein the first member is a fixed shoe, the'second member is a driven disk, and the third member is a driven disk.

4. Apparatus as recited in claim ll, wherein the second member contacts the workpiece approximately in one direction away from the first member and the third member in the first position contacts the workpiece approximately in the other direction and in the second position at approximately 90 in the other direction.

References Cited by the Examiner UNITED STATES PATENTS 2/38 Briney 51-103 6/45 Cramer 51'103 XR 

1. APPARATUS FOR SUPPORTING A WORKPIECE HAVING A SURFACE OF REVOLUTION, COMPRISING (A) A BASE, (B) A FIRST MEMBER MOUNTED ON THE BASE ADAPTED TO CONTACT A POSITION ON THE SURFACE OF THE WORKPIECE, (C) A SECOND MEMBER MOUNTED ON THE BASED ADAPTED TO CONTACT THE SURFACE OF THE WORKPIECE AT A POSITION SUBSTANTIALLY SPACED FROM THE POSITION OF CONTACT OF THE FIRST MEMBER, (D) A THIRD MEMBER MOUNTED ON THE BASE ADAPTED TO CONTACT THE SURFACE OF THE WORKPIECE AT A FIRST POSITION SUBSTANTIALLY OPPOSITE THE MIDPOINT BETWEEN THE POSITION OF CONTACT OF THE FIRST MEMBER AND THE POSITION OF CONTACT OF THE SECOND MEMBER, AND (E) AN ARTICULATED ARM HAVING TWO HINGED PORTIONS SPRING-BASED RELATIVE TO EACH OTHER AND ALSO TO THE BASE SUPPORTING THE THIRD MEMBER IN SUCH A MANNER THAT, ON OCCASION, IT CONTACTS THE SURFACT OF THE WORKPIECE AT A SECOND POSITION WHICH IS SUBSTANTIALLY OPPOSITE THE POSITION OF CONTACT OF THE SECOND MEMBER AND IS MOVABLE RADIALLY AWAY FROM THE SAID SECOND POSITION 